Amino acid

Humans can synthesise 11 of the basic set of 20 amino acids. The rest must be obtained from the diet: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine are therefore known as ‘essential’ amino acids.

Synthesis of those amino acids that can be made proceeds as follows: the carbon skeleton usually arises from metabolic intermediates such as oxaloacetate and pyruvate; amino acids are donated by other amino acids in transamination reactions; extra amino groups are sometimes derived from ammonia after first being incorporated into glutamate by the enzyme glutamate dehydrogenase.